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Category Archives: Stars

It is true that all living things come from stardust. In about 5 billion years, our Sun will have swelled to a red giant and engulfed the inner planets, ready to explode in a supernova. Supernovae enrich the interstellar medium with high mass elements, like iron and calcium. The high energy from supernovae also triggers formation of new stars. On average, supernovae occur only about once every 50 years in the Milky Way Galaxy. They are rare events— so rare that the last one in the Milky Way was discovered in 1604 (SN 1604, or Kepler’s Supernova)— spectacularly luminous and extremely destructive. In fact, supernovae can cause bursts of radiation more luminous than entire galaxies and emit as much energy as the Sun will in its entire lifespan! In a supernova, most of the star’s material is expelled into space at speeds up to 30,000 m/s. The shock wave passes through the supernova remnant, a huge expanding shell of gas and dust. Supernova are caused either by the sudden gravitational collapse of a supergiant star (Type I Supernova) or a white dwarf accreting enough mass or merging with a binary companion to undergo nuclear fusion (Type II Supernova). White dwarfs are very dense stars that do not have enough mass to become a neutron star (formed from supernova remnant, stars comprising almost entirely of neutrons). Supernovae can be used as standard candles (objects with known luminosity). For instance, the dimming luminosity of distant supernovae supports the theory that the expansion of the universe is accelerating. Now, with powerful telescopes like Hubble, many supernovae are discovered each year. How perfectly supernovae represent the circle of life: from death comes life!

History of Supernova Observations (Milky Way)

SN185 by Chinese astronomers

SN1006 by Chinese and Islamic astronomers

SN1054 (caused Crab Nebula)

SN1572 by Tycho Brahe in Cassiopeia

SN1604 by Johannes Kepler

* Supernova (SN) are named by the year they are discovered; if more than one in one year, the name is followed by a capital letter (A, B, C, etc.), and if more than 26, lowercase paired letters (aa, ab, etc.) are used

Strong Nuclear Forces: protons in the nucleus repel by electrical forces, but strong nuclear forces, which can only occur at close distances, keep the atom together. As temperature rises, protons move faster. When 2 protons fuse, the output is 1 neutron, 1 positron, and 1 neutrino.

0.7% of the total mass of 4 protons is converted into energy, while 99.3% results in 1 helium nucleus. Some of the mass is converted into energy. Since E = mc², a little mass and release tremendous energy. While at rest, however, energy is equal to mass.

CNO Cycle

CNO (Carbon-Nitrogen-Oxygen) Cycle

The CNO Cycle is the main nuclear burning chain in main sequence stars hotter than the Sun. Using carbon as a catalyst to convert hydrogen into helium, the CNO cycle also converts 7% of hydrogen’s mass into energy; hydrogen fuses with carbon to form helium. 10% of the Sun’s nuclear fusion reactions is from the CNO Cycle. In 1967, Hans Bethe theorized on the energy production in stars.

Peak wavelength of electromagnetic radiation is related to temperature

Wien’s Law: W = 0.00290/T

As temperature increases, wavelength decreases

The hotter an object, the bluer the radiation

To determine density

The thicker the spectral line, the greater the abundance of the chemical element present

To determine motion

Doppler shift of spectral lines

Red Shift = moving away

Blue Shift = moving closer

To determine distance

Measured in light years (ly) – distance light travels in one year and parsecs (pc) – one parsec is 3.26 light years

Parallax: the only direct measure of stellar distance, the angle across the sky that a star seems to move with respect to a background of distant stars) between two observation points at the ends of a baseline of one astronomical unit (A.U.); a star one parsec from Earth has a parallax of one arc second

BROWN DWARFS: stars too small to perform nuclear fusion (no new energy) but too massive to be a planet

Masses range from 13 Jupiter-masses to 25 Jupiter-masses

Radius same as Jupiter but be up to 60-90 Jupiter masses

Some emit x-rays

All glow red in the infrared spectra until they cool off to 1,000 K

In 1995, the first brown dwarf, Teide 1 of the Pleiades cluster (M8 star), was discovered by the Spanish Observatory of Roque de los Muchachos and verified. Most brown dwarfs belong to spectral types L and T, which contain cooler stars than spectral type M. So far, more than 1,000 brown dwarfs have been discovered.

Remnant of cores of massive stars, left over after the core collapses in the supernova explosion

1.5x more massive than the Sun, only 10 km in radius

1 cm³ = 1 billion tons

How to Detect Them

Pulsars: spinning neutron stars that emit radio waves

X-Ray Binaries: in a binary star system, accretes matter from the other star

Pulsar

Pulsars: In 1967, Jocelyn Bell discovered that a radio source emitted regular “pulses” of radio waves every 1,337 seconds, like clockwork. A pulsar is a rotating neutron star (e.g. Crab Pulsar). Its strong magnetic field generates radio emission. Since a beam of radio waves “sweeps” past us as the star rotates, the neutron star appears to change in luminosity.

X-Ray Binary

X- Ray Binaries: In a binary star system, a neutron star can accrete mass spilling off of a companion star. There may also be black holes in x-ray binaries (e.g. GS2000+25)

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Astronomy: To Infinity and Beyond! Welcome to "The Cosmos." I will take you on a journey through our solar system, galaxy, and the Universe! You will be updated with current events in astronomy. Please click on the picture above to visit my blog on poetry, writings, and musings!

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References for photos used from websites can be found under the "References" page. Photo credit: news sites (reference included in post), NASA (most images used), and Google (for artists' view of objects unable to be photographed).